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Mixed oxide
About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.
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TL;DR: The solubility of a range of metal oxides in a eutectic mixture of urea/choline chloride is quantified, and it is shown that the dissolved metals can be reclaimed from a mixed metal oxide matrix using electrodeposition.
Abstract: The solubility of a range of metal oxides in a eutectic mixture of urea/choline chloride is quantified, and it is shown that the dissolved metals can be reclaimed from a mixed metal oxide matrix using electrodeposition.
304 citations
TL;DR: In this paper, the catalytic performance of mixed oxide catalysts can be improved significantly by proper selection of metal oxide (M x O y ) loading and composition, which can be attributed to the better dispersion of the active M x o y phases, their increased reducibility, and their lower tendency to form coke deposits under reaction conditions.
Abstract: The catalytic oxidation of toluene has been investigated over binary mixtures of copper, manganese and cerium oxides supported on high surface area γ-Al 2 O 3 in comparison with the corresponding single metal oxide components. Catalysts were synthesized with the impregnation method and were characterized with respect to their specific surface area (BET method), phase composition and mean crystallite size (XRD technique), reducibility (H 2 -TPR) and adsorption/desorption characteristics toward toluene (TPD followed by TPO). Results obtained using a feed composition consisting of 1000 ppm toluene in air showed that the catalytic performance of mixed oxide catalysts can be improved significantly by proper selection of metal oxide (M x O y ) loading and composition. The intrinsic activity of optimized catalysts, measured under differential reaction conditions, was found to be significantly higher compared to that of their single-component counterparts. This has been attributed to the better dispersion of the active M x O y phases, their increased reducibility (reactivity of surface oxygen), and their lower tendency to form coke deposits under reaction conditions. Addition of a second VOC (propane) or water vapor in the feed affected differently the activity of optimized-mixed oxide catalysts. As a general trend, inhibition by the presence of propane was more pronounced for CeO 2 -containing samples whereas the presence of H 2 O affected mainly the CuO x -containing catalysts. It is concluded that the VOC oxidation activity of Al 2 O 3 -supported mixed oxide catalysts is determined by the reducibility of the dispersed active phases, which may be controlled by proper selection of M x O y nature, loading and composition.
302 citations
TL;DR: In this article, a modified coprecipitation method was used for the complete oxidation of formaldehyde and the MnO x −CeO 2 mixed oxides with a Mn/(Mn+Ce) molar ratio of 0.5 exhibited the highest catalytic activity among the Mn O x -Ce O 2 mixed oxide, while the Pt precursors and reduction temperature greatly affected the catalytic performance.
Abstract: MnO x –CeO 2 mixed oxides with a Mn/(Mn + Ce) molar ratios of 0–1 were prepared by a modified coprecipitation method and investigated for the complete oxidation of formaldehyde. The MnO x –CeO 2 with Mn/(Mn + Ce) molar ratio of 0.5 exhibited the highest catalytic activity among the MnO x –CeO 2 mixed oxides. Structure analysis by X-ray powder diffraction and temperature-programmed reduction of hydrogen revealed that the formation of MnO x –CeO 2 solid solution greatly improved the low-temperature reducibility, resulting in a higher catalytic activity for the oxidation of formaldehyde. Promoting effect of Pt on the MnO x –CeO 2 mixed oxide indicated that both the Pt precursors and the reduction temperature greatly affected the catalytic performance. Pt/MnO x –CeO 2 catalyst prepared from chlorine-free precursor showed extremely high activity and stability after pretreatment with hydrogen at 473 K. 100% conversion of formaldehyde was achieved at ambient temperature and no deactivation was observed for 120 h time-on-stream. The promoting effect of Pt was ascribed to enhance the effective activation of oxygen molecule on the MnO x –CeO 2 support.
300 citations
TL;DR: In this paper, rare-earth ion doping has been used to increase the surface area of rare earth-modified ceria (CeO 2 ) and rare earth modified ceria(CeReO x with Re-=La, Pr, Sm, Y) catalysts.
Abstract: Ceria (CeO 2 ) and rare-earth modified ceria (CeReO x with Re = La, Pr, Sm, Y) catalysts are prepared by nitrate precursor calcination and are characterised by BET surface area, XRD, H 2 -TPR, and Raman spectroscopy. Potential of the catalysts in the soot oxidation is evaluated in TGA with a feed gas containing O 2 . Seven hundred degree Celsius calcination leads to a decrease in the surface area of the rare-earth modified CeO 2 compared with CeO 2 . However, an increase in the meso/macro pore volume, an important parameter for the soot oxidation with O 2 , is observed. Rare-earth ion doping led to the stabilisation of the CeO 2 surface area when calcined at 1000 °C. XRD, H 2 -TPR, and Raman characterisation show a solid solution formation in most of the mixed oxide catalysts. Surface segregation of dopant and even separate phases, in CeSmO x and CeYO x catalysts, are, however, observed. CePrO x and CeLaO x catalysts show superior soot oxidation activity (100% soot oxidation below 550 °C) compared with CeSmO x , CeYO x , and CeO 2 . The improved soot oxidation activity of rare-earth doped CeO 2 catalysts with O 2 can be correlated with the increased meso/micro pore volume and stabilisation of external surface area. The segregation of the phases and the enrichment of the catalyst surface with unreducible dopant decrease the intrinsic soot oxidation activity of the potential CeO 2 catalytic sites. Doping CeO 2 with a reducible ion such as Pr 4+/3+ shows an increase in the soot oxidation. However, the ease of catalyst reduction and the bulk oxygen-storage capacity is not a critical parameter in the determination of the soot oxidation activity. During the soot oxidation with O 2 , the function of the catalyst is to increase the ‘active oxygen’ transfer to the soot surface, but it does not change the rate-determining step, as evident from the unchanged apparent activation energy (around 150 kJ mol −1 ), for the catalysed and un-catalysed soot oxidation. Spill over of oxygen on the soot surface and its subsequent adsorption at the active carbon sites is an important intermediate step in the soot oxidation mechanism.
288 citations
TL;DR: In this article, the yolk-shelled Ni-Co mixed oxide nanoprisms with tunable composition have been prepared by simple thermal annealing in air, and the resulting Ni0.37Co oxide sample delivers very high specific capacitance of over 1000 F g−1 at a current density of 10 A g −1 with remarkably high capacitance retention of 98% after 15 000 cycles.
Abstract: Yolk-shelled particles with tailored physical and chemical properties are attractive for electrochemical energy storage. Starting with metal acetate hydroxide with tetragonal prism-like shapes, yolk-shelled Ni–Co mixed oxide nanoprisms with tunable composition have been prepared by simple thermal annealing in air. It is found that the yolk-shelled structure is formed due to the fast thermally driven contraction process. With the favorable porous structure and composition, these yolk-shelled Ni–Co oxide particles manifest greatly enhanced electrochemical properties when evaluated as electrodes for both hybrid supercapacitors and lithium ion batteries. In particular, the resultant Ni0.37Co oxide sample delivers very high specific capacitance of over 1000 F g−1 at a current density of 10 A g−1 with remarkably high capacitance retention of 98% after 15 000 cycles.
284 citations